The father of a teenager who spent 10 hours with a bomb chained around her neck has revealed might not have called police if he had realised the incident was an attempted extortion.

Wealthy Australian businessman Bill Pulver said he might have paid the ransom rather than call the police to avoid risking his daughter's safety further. Neither knew at the time the bomb was fake.

Mr Pulver spoke outside New South Wales state District Court, where investment banker Paul Peters, 52, appeared for a sentencing hearing after pleading guilty to breaking into the Pulver mansion in Sydney and attaching the bomb. He faces up to 20 years in prison when the hearing continues next week.

"If I had known there was an extortion letter, I ask myself the question: Would I have actually rung the police?" Mr Pulver said. "I'm really not sure what I would have done," he added. "He very nearly got away with it."

Peters admitted to entering the family mansion wearing a ski mask and wielding a baseball bat on August 3, 2011 before the device to then-18-year-old Madeleine Pulver, who had been home alone studying for school exams. She phoned her father after Peters left the house, unaware that a note was attached to the fake collar bomb demanding an unspecified sum of money and warning that the device would explode if tampered with.

Mr Pulver raised the alarm, sparking a 10-hour police bomb squad operation that found the device was harmless, and subsequently discovered the ransom note.

Peters, who travelled frequently between the United States and Australia on business, fled to the US and was arrested nearly two weeks later at the Louisville, Kentucky, home of his former wife. He was extradited to Australia and has remained in prison custody since.

Two psychiatrists gave differing opinions on Peters' mental state at the time of the incident, which Peters has said he cannot remember.

Psychiatrist Jonathan Phillips said that he believed Peters was in a psychotic state during the crime. Peters was one of the most difficult and complex cases he had ever assessed, he said. "It's unusual for a person with a long and seemingly untroubled life and record to then commit an extremely callous and dangerous act," Phillips said.He said Peters suffered from a bipolar disorder and was in an intermittent psychotic state in the weeks or months prior to the incident.

Psychiatrist Stephen Allnutt said he did not believe Peters was suffering from psychosis. "When you look at the (police) interview ... he's a fairly intelligent man who doesn't demonstrate any symptoms of mental illness," he said.